This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In E. coli the Min system (MinD, MinD and MinE) spatially regulates cell division by restricting Z ring assembly to a midcell location. MinD is a membrane associated ATPase, which is part of a larger family of ATPases. These include the family of Par proteins and nitrogenase iron proteins. After FtsZ (a tubulin homologue), MinD is the most highly conserved component of the cell division machinery. In the presence of ATP, MinD dimerizes, binds to the membrane and recruits MinC. MinD binds to MinC inhibiting cell division. Consistent with their function, the min system has been found to oscillate from cell pole to cell pole. The MinD ATPase is critical to the oscillation of the Min proteins. It has been proposed that this behavior masks potential division sites and localizes the cell division machinery to midcell. Clearly the determination of the structure of the active ATP-dependent dimer form of MinD will provide significant insight into the functional role of this important molecule. Previous structures of MinD related proteins are monomers from Archaea sp. Therefore the biologically relevant ATP dependent dimer structure is unknown. These archaeal proteins have little homology to the E. coli protein (